Lubricant compositions for SI-AL alloy surfaces and methods for using

ABSTRACT

A lubricant composition including: (A) greater than 50 wt % of a base stock based on the total weight of the composition selected from the group consisting of that of a Group III base oil, a Group IV base oil, and a combination thereof; and (B) one or more additional components. The one or more additional components are selected from the group consisting of: (i) one or more high or medium base carboxylate detergents; (ii) one or more low base carboxylate detergents, wherein the low base carboxylate detergent is present at a level of 0.60 wt % or less based on the total weight of the composition; (iii) one or more low base carboxylate detergents and one or more aromatics-containing base stock(s); and (iv) one or more phenolic detergents.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser. No. 61/579,230, filed on Dec. 22, 2011; which is incorporated herein in its entirety by reference.

FIELD

The present disclosure relates to lubricant compositions. The present disclosure further relates to lubricant compositions useful in lubricating Si—Al alloy surfaces. The present disclosure further relates to a method for lubricating a Si—Al alloy surface. The present disclosure further relates to a method for lubricating a cylinder liner and a piston ring. The present disclosure further relates to a method for lubricating rubbing surfaces of dissimilar metallic materials.

BACKGROUND

Improving energy efficiency and fuel economy in automobiles is a goal of manufacturers worldwide. One means of improving fuel economy is in improvement of lubrication systems. Fuel economy can be enhanced by lowering crankcase engine oil viscosity. However, lowering engine oil viscosity can cause excessive engine wear and friction, thus lowering engine durability and shortening engine life. Engine friction impacts both fuel efficiency and engine wear. Approximately 50% of all friction-related energy losses in an internal combustion engine are attributed to friction between cylinder liners and piston rings.

Modern high-performance engines utilize advanced surfaces on cylinder liners to provide improved mechanical performance. For example, Si—Al (silicon-aluminum) alloy surfaces provide enhanced performance with respect to oil consumption, ring/piston tension, heat transfer, and material weight reduction. The Si—Al alloys consist of nanoparticles and microparticles of silicon in a matrix of aluminum alloy metal. Lubrication performance is very sensitive to metallurgy and environment. The use of Si—Al cylinder liners in combination with steel piston rings (often modified, for example, by nitriding or coating with chrome, ceramic, or DLC materials) has presented new and different lubrication challenges compared to that encountered with traditional iron alloy cylinder liners. With two rubbing surfaces of dissimilar metallurgy, for instance Si—Al alloy (cylinder liner) and ferrous alloy (steel piston ring), certain traditional classes of lubricant performance additives that perform effectively in the case of steel-on-steel do not always perform effectively in the case of Si—Al on steel. In particular, certain detergents containing oxygen-based functional groups can cause high rubbing friction and can cause unacceptably high wear of Si—Al alloy surfaces. In some instances, carboxylate-type detergents, e.g., low-base salicylates, and phenolic-type detergents, e.g. phenates, can cause excessively high rubbing friction that can lead to excessive Si—Al alloy wear.

It would be desirable to have a lubrication composition that would be effective in controlling or reducing friction in engines that have Si—Al (silicon-aluminum) alloy surfaces. It would also be desirable to have a method for lubricating such surfaces.

SUMMARY

According to the present disclosure, there is provided a lubricant composition. The composition has the following: (A) greater than 50 wt % of a base stock based on the total weight of the composition selected from the group consisting of a Group III base stock, a Group IV base stock, and a combination thereof and (B) one or more additional components. The one or more additional components is selected from the group consisting of (i) one or more high or medium base carboxylate detergents; (ii) one or more low base carboxylate detergents, wherein the one or more low base carboxylate detergents is present at a level of less than 0.60 wt % based on the total weight of the composition; (iii) one or more low base carboxylate detergents and one or more aromatics-containing base stock(s) and wherein the value of “A” is less than or equal to 190; and (iv) one or more phenolic detergents, wherein if the one or more phenolic detergents is one or more phenate detergents, the one or more phenate detergent is present at a level of less than 5 wt % based on the total weight of the lubricant composition. “A” is determined according to the following formula:

$A = \frac{{wt}\mspace{14mu} \% \mspace{14mu} {low}\mspace{14mu} {base}\mspace{14mu} {carboxylate}\mspace{14mu} {detergent}}{\% \mspace{14mu} {base}\mspace{14mu} {oil}\mspace{14mu} {proton}\mspace{14mu} {aromaticity}}$

wherein “wt % low base carboxylate detergent” is determined by the weight based on the total weight of the lubricant composition; and wherein“% base oil proton aromaticity” is the percentage of aromatics present in the base oil as determined by ASTM D5292, ¹H NMR. Contributions to the total % base oil proton aromaticity include base stock(s) used to formulate the finished lubricant, base stock(s) used as diluents or solubilizers in viscosity modifier polymer preblends, and base stock(s) used in performance additive packages. The lubricant composition exhibits a frictional coefficient of less than or equal to 0.31 in an SRV Screener Test.

According to the present disclosure, there is provided a method for lubricating a surface of a Si—Al alloy. The lubricant composition is applied or otherwise exposed to the surface.

According to the present disclosure, there is provided a method of lubricating a cylinder liner of a composite of silicon microparticles in a silicon-aluminum alloy matrix and a nitrided steel piston ring. The method has the step of applying to rubbing surfaces of the liner and the piston ring the lubricant composition.

According to the present disclosure, there is provided a method of lubricating rubbing surfaces of dissimilar metallic materials in which one rubbing surface has a higher Vickers hardness than the other rubbing surface. The method has the step of applying to rubbing surfaces of the liner and the piston ring the lubricant composition.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a plot of the characteristic parameter “A” vs. measured Silitec SRV frictional coefficients indicating regions of acceptable Silitec SRV frictional performance.

DETAILED DESCRIPTION

All numerical values within the detailed description and the claims herein are modified by “ ” or “approximately” the indicated value, and take into account experimental error and variations that would be expected by a person having ordinary skill in the art.

The lubricant compositions of the present disclosure impart an unexpected reduction of SRV friction on Si—Al alloy surfaces. In particular, the lubricant compositions impart an unexpected enhancement of lubrication performance on Si—Al alloy surfaces on cylinder liner surfaces of cylinder liner/piston ring assemblies. In one embodiment, lubricant compositions employ a base oil with a major portion of a Group III and/or Group IV base stock(s) and particular levels/ranges of low-base carboxylate detergent(s) or aromatics-containing base stock(s) in particular ratios with a low-base carboxylate detergent(s).

The lubricant compositions of the present disclosure are particularly useful on Si—Al alloy surfaces. An example of a useful Si—Al alloy is a hypereutectic Si—Al alloy in which micron or submicron sized silicon (Si) particles are embedded in an aluminum (Al) alloy matrix. Hypereutectic Si—Al alloys and processes for preparing them are set forth by way of example in U.S. Pat. No. 6,994,147 B2 and U.S. Published Patent Application No. 2004/0055724 A1, which are incorporated herein by reference. Other Si—Al alloy materials that may be advantageously used with the lubricant compositions include, for example, Silitec, Alusil, Lokail, DiASil, Morcaosil, AlBoND. Si—Al alloys may be used as monolithic structures or as layered coatings on suitable substrates.

A variety of base stocks are useful in the lubricating compositions of the present disclosure. Useful lubricating base stocks include natural oils and synthetic oils. Natural and synthetic oils (or mixtures thereof) can be used as unrefined, refined, or rerefined (the latter is also known as reclaimed or reprocessed oil). Unrefined oils are those obtained directly from a natural or synthetic source and used without added purification. These include shale oil obtained directly from retorting operations, petroleum oil obtained directly from primary distillation, and ester oil obtained directly from an esterification process. Refined oils are similar to the oils discussed for unrefined oils except refined oils are subjected to one or more purification steps to improve at least one lubricating oil property. Purification processes known in the art include solvent extraction, secondary distillation, acid extraction, base extraction, filtration, and percolation. Rerefined oils are obtained by processes analogous to refined oils but using oil that has been previously used as feedstock.

Groups I, II, III, IV and V are broad categories of base stocks developed and defined by the American Petroleum Institute (API Publication 1509) to create guidelines for lubricant base stocks. Group I base stocks have a viscosity index of 80 to 120 and contain greater than 0.03% sulfur and less than 90% saturates. Group II base stocks have a viscosity index of 80 to 120, and contain less than or equal to 0.03% sulfur and greater than or equal to 90% saturates. Group III stocks have a viscosity index greater than 120 and contain less than or equal to 0.03% sulfur and greater than 90% saturates. Group IV includes polyalphaolefins (PAO). Group V base stock includes base stocks not included in Groups I-IV. Table 1 below summarizes properties of each of these five groups.

TABLE 1 Base Stock Properties Saturates Sulfur Viscosity Index Group I <90 and/or >0.03% and ≧80 and <120 Group II ≧90 and ≦0.03% and ≧80 and <120 Group III ≧90 and ≦0.03% and ≧120 Group IV Polyalphaolefins (PAO) Group V All other base stocks not included in Groups I, II, III or IV

Natural oils include animal oils, vegetable oils (castor oil and lard oil, for example), and mineral oils. Animal and vegetable oils possessing favorable thermal oxidative stability can be used. Of the natural oils, mineral oils are preferred. Mineral oils vary widely as to their crude source, for example, as to whether they are paraffinic, naphthenic, or mixed paraffinic-naphthenic. Oils derived from coal or shale are also useful. Natural oils vary also as to the method used for their production and purification, for example, their distillation range and whether they are straight run or cracked, hydrorefined, or solvent extracted.

Additional well known base stocks include Group II and/or Group III hydroprocessed or hydrocracked base stocks and synthetic oils, such as polyalphaolefins, alkyl aromatics and synthetic esters.

Group V base stocks, for example, esters, alcohols, ethers, acids, and other O, S, and N containing base stocks are useful in the lubricant compositions.

Synthetic oils include hydrocarbon oils. Hydrocarbon oils include oils of polymerized and interpolymerized olefins (polybutylenes, polypropylenes, propylene isobutylene copolymers, ethylene-olefin copolymers, and ethylene-alphaolefin copolymers, for example). Polyalphaolefin (PAO) oil base stocks are commonly used in synthetic hydrocarbon oils. By way of example, PAOs derived from C8, C10, C12, and C14 olefins and mixtures thereof may be utilized. See U.S. Pat. Nos. 4,956,122; 4,827,064; and 4,827,073.

The number average molecular weights of the PAOs typically vary from 250 to 3,000. The PAOs are typically comprised of relatively low molecular weight hydrogenated polymers or oligomers of alphaolefins that include, but are not limited to, C2 to C32 alphaolefins with the C8 to C16 alphaolefins, such as 1-octene; 1-decene, and 1-dodecene being preferred. The preferred polyalphaolefins are poly-1-octene, poly-1-decene, and poly-1-dodecene and mixtures thereof and mixed olefin-derived polyolefins. However, the dimers of higher olefins in the range of C14 to C18 may be used to provide low viscosity base stocks of acceptably low volatility. Depending on the viscosity grade and the starting oligomer, the PAOs may be predominantly trimers and tetramers of the starting olefins, with minor amounts of the higher oligomers, having a viscosity range of 1 to 12 cSt. PAO's may also be made at higher viscosities up to 3000 cSt (100° C.).

The PAO fluids may be conveniently made by the polymerization of an alphaolefln in the presence of a polymerization catalyst, such as Friedel-Crafts catalysts. Useful catalysts include, for example, aluminum trichloride; boron trifluoride and complexes of boron trifluoride with water; alcohols such as ethanol, propanol or butanol; and carboxylic acids or esters such as ethyl acetate or ethyl propionate. For example, the methods disclosed by U.S. Pat. No. 4,149,178 or U.S. Pat. No. 3,382,291 may be conveniently used herein. Other descriptions of PAO synthesis are found in the following: U.S. Pat. Nos. 3,742,082; 3,769,363; 3,876,720; 4,239,930; 4,367,352; 4,413,156; 4,434,408; 4,910,355; 4,956,122; and 5,068,487. The dimers of the C14 to C18 olefins are described in U.S. Pat. No. 4,218,330.

The hydrocarbyl aromatics can be used as a base stock or base stock component and can be any hydrocarbyl molecule that contains at least 5% of its weight derived from an aromatic moiety such as a benzenoid moiety or naphthenoid moiety, or their derivatives. These hydrocarbyl aromatics include alkyl benzenes, alkyl naphthalenes, alkyl diphenyl oxides, alkyl naphthols, alkyl diphenyl sulfides, alkylated bis-phenol A, and alkylated thiodiphenol. The aromatic can be mono-alkylated, dialkylated, and polyalkylated. The aromatic can be mono- or poly-functionalized. The hydrocarbyl groups can also be comprised of mixtures of alkyl groups, alkenyl groups, alkynyl, cycloalkyl groups, cycloalkenyl groups and other related hydrocarbyl groups. The hydrocarbyl groups can range from C6 up to C60, with a range of C8 to C20 often being preferred. A mixture of hydrocarbyl groups is often preferred, and up to three such substituents may be present. The hydrocarbyl group can optionally contain sulfur, oxygen, and/or nitrogen containing substituents. The aromatic group can also be derived from natural (petroleum) sources provided at least 5% of the molecule is comprised of an above-type aromatic moiety. Aromatics-containing base stock(s) include those of Group I, Group II, and Group V. Further, the aromatics-containing base stock may be an alkylated naphthalene. Viscosities at 100° C. of approximately 3 cSt to 50 cSt are preferred, with viscosities of approximately 3.4 cSt to 20 cSt often being more preferred for the hydrocarbyl aromatic component. In one embodiment, an alkyl naphthalene in which the alkyl group is primarily comprised of 1-hexadecene is used. Other alkylates of aromatics can be advantageously used. Naphthalene or methyl naphthalene, for example, can be alkylated with olefins such as octene, decene, dodecene, tetradecene or higher, and mixtures of similar olefins. Useful concentrations of hydrocarbyl aromatic in a lubricant oil composition can be up to 25%, preferably up to 20%, and more preferably up to 15% depending on the application.

The base stocks selected from among Group III, Group IV, and combinations thereof, may preferably be present at 50 wt % or more, or more preferably may be present at 60 wt % or more, or even more preferably, may be present at 70 wt % or more based on the total weight of the lubricant composition. The base stocks selected from among Group III, Group IV, and combinations thereof, may be further characterized as having a viscosity index (VI) of equal to or greater that 125, and, in some instances, preferably equal to or greater than 130. Further, the base stocks from among Group III, Group IV, and combinations thereof, may also be characterized as having solvency as defined by an aniline point of equal to or greater than 110, and in some instances, preferably equal to or greater than 115. Further, the aniline point for these base stocks may be equal to or greater than 120.

Useful lubricant base stocks preferably exhibit a pour point of less than 10° C., more preferably less than 0° C., and most preferably less than −10° C. according to ASTM D 97. The lubricant base stocks preferably exhibit a kinematic viscosity at 40° C. from 4 to 80,000 centi-Stokes (cSt) and more preferably from 4 cSt to 50,000 cSt at 40° C. according to ASTM D445. The lubricant base stocks preferably exhibit a kinematic viscosity at 100° C. of 1.5 to 5,000 cSt, more preferably 2 cSt to 3,000 cSt, and most preferably 2 cSt to 500 cSt. Low viscosity lubricant base stocks are particularly useful in automotive motor oil applications, namely those with kinematic viscosities at 100° C. from 2 cSt to 15 cSt and more typically 2 cSt to 8 cSt. Low viscosity lubricant base stocks are particularly useful for SAE 0W-20 and SAE 0W-30 motor oils.

The lubricant compositions of the present disclosure have one or more detergent additives of carboxylate detergents, which may be of a low base, or medium base, or high base carboxylate detergent or combinations thereof. Low base carboxylate detergents exhibit a total base number (TBN) of ≦100 mgKOH/g. Medium and high base carboxylate detergents exhibit a total base number (TBN) of >100 mgKOH/g. Salicylate detergents are preferred. Calcium salicylate detergents are often more preferred.

When low base carboxylate detergents are present, the amount of low base carboxylate detergent employed in the lubricant compositions will vary depending on the embodiment. For instance, in one embodiment, the level can be ≦0.60 wt %. The detergency of the lubricant compositions can be enhanced with the inclusion of medium or high base carboxylate detergents, preferably at levels up to 5 wt %. Weight percent (wt %) herein is based on the total weight of the lubricant composition.

Carboxylate detergents may be prepared by reacting a basic metal compound with at least one carboxylic acid compound and removing free water from the reaction product. These compounds may be overbased to produce the desired TBN level. Detergents made from salicylic acid are one preferred class of detergents derived from carboxylic acids. Useful salicylates include long chain alkyl salicylates. One useful family of compositions is of the formula

wherein R is a hydrogen atom or an alkyl group having 1 to 30 carbon atoms, n is an integer from 1 to 4, and M is an alkaline earth metal. Preferred R groups are alkyl chains of at least C₁₁, preferably C₁₃ or greater. R may be optionally substituted with substituents that do not interfere with the detergent's function. M is preferably, calcium, magnesium, or barium. More preferably, M is calcium.

Hydrocarbyl-substituted salicylic acids may be prepared from phenols by the Kolbe reaction. See U.S. Pat. No. 3,595,791, which is incorporated herein by reference in its entirety, for additional information on synthesis of these compounds. The metal salts of the hydrocarbyl-substituted salicylic acids may be prepared by double decomposition of a metal salt in a polar solvent such as water or alcohol.

In another embodiment, one or more phenolic-type detergents may be used. The detergents may be a phenate detergent, wherein the phenate detergent is present at a level of less than 5 wt % based on the total weight of the lubricant composition. In particular, metal salts of these phenolic type detergents are useful, and the metals in such salts can comprise alkali metals, alkaline earth metals, boron, or titanium. In some instances, the calcium derivatives of these detergents are often preferred.

Alkaline earth phenates are another useful class of phenolic detergents. These detergents can be made by reacting alkaline earth metal hydroxide or oxide (CaO, Ca(OH)₂, BaO, Ba(OH)₂, MgO, Mg(OH)₂, for example) with an alkyl phenol or sulfurized alkylphenol. Useful alkyl groups include straight chain or branched C₁-C₃₀ alkyl groups, preferably, C₄-C₂₀. Examples of suitable phenols include isobutylphenol, 2-ethylhexylphenol, nonylphenol, dodecyl phenol, and the like. It should be noted that starting alkylphenols may contain more than one alkyl substituent that are each independently straight chain or branched. When a non-sulfurized alkylphenol is used, the sulfurized product may be obtained by methods well known in the art. These methods include heating a mixture of alkylphenol and sulfurizing agent (including elemental sulfur, sulfur halides such as sulfur dichloride) and then reacting the sulfurized phenol with an alkaline earth metal base.

In another embodiment, the low base carboxylate detergents are alkylated mono-carboxylates. In another embodiment, the low base carboxylate detergents are alkylated mono-carboxylates. In either case, the carboxylate functional group may comprise a carboxylic acid, ester, amide, imide, anhydride, halide, or salt, whereby the salt may include organic cations, amine type cations, and metal type cations, such as alkali, alkaline earth, and transition metals.

In another embodiment, the carboxylate detergents are salicylate detergents and the low base carboxylate detergents are low base salicylate detergents. In particular, metal salts of these carboxylate and salicylate detergents are useful, and the metals in such salts comprise alkali metals, alkaline earth metals, boron, titanium, or transition metals. In other embodiments, the calcium derivatives of these detergents can be preferred.

In another embodiment, the carboxylate detergents are salicylate detergents, wherein the TBN contribution from the low base salicylate detergent to the total lubricant composition is less than 0.4 mg/KOH.

Phenol-derived detergents such as saligens and salixarates may also be employed. The concentration of these detergents in a lubricant is preferably limited such that the lubricant composition demonstrates frictional coefficients of less than or equal to 0.31 in an SRV Screener Test.

Lubricant compositions of the present disclosure may optionally include other conventional lubricant additives, such as antioxidants, anti-wear additives, pour point depressants, viscosity index modifiers, friction modifiers, de-foaming agents, corrosion inhibitors, wetting agents, rust inhibitors, and seal swell agents. The additives may be incorporated to make a finished lubricant product that has desired viscosity and physical properties. Typical additives used in lubricant formulation can be found in the book “Lubricant Additives, Chemistry and Applications”, Ed. L. R. Rudnick, Marcel Dekker, Inc. 270 Madison Ave. New York, N.J. 10016, 2003

Lubricant compositions of the present disclosure are useful as oils or greases for any device or apparatus requiring lubrication of moving and/or interacting mechanical parts, components, or surfaces. Useful apparatuses include engines and machines. The lubricant compositions are most suitable for use in the formulation of automotive crank-case lubricants, automotive gear oils, transmission oils, many industrial lubricants including circulation lubricant, industrial gear lubricants, grease, compressor oil, pump oils, refrigeration lubricants, hydraulic lubricants, metal working fluids. Lubricant compositions are particularly useful in automotive applications as crank-case oil, i.e., motor oil or engine oil.

The lubricant compositions of this disclosure are particularly useful in any mechanical system in which rubbing surfaces of dissimilar materials exist. Mechanical components that may have dissimilar materials in such systems include bearings (e.g. sliding, rolling, reciprocating), gears, pumps, cylinder liners, and piston rings. The lubricant compositions are particularly useful, for instance, in engines and powerplants used in transportation vehicles, such as internal combustion engines, hybrid engines and systems, pneumatic engines and systems, electrical engines and systems, and alternate fuel engines. The lubricant compositions are also useful in conjunction with alternative fuels such as biofuels and alcohol-type fuels.

An example of two rubbing dissimilar surfaces are the combination of an Si—Al type alloy and a ferrous type ahoy. Other dissimilar materials can be distinguished by their relative hardness. One of the paired rubbing surfaces is “harder” and the other of the pair is “softer”. For example, the ferrous type surface composition can include different grades of iron and steel, irons and steels modified by nitriding or other ion-implantation methods, irons or steels coated with ceramic type materials, chrome alloys, other hard alloys, and DLC and its derivatives. In addition, a non-ferrous type surface can consist of materials and metal alloys that are softer or more ductile than that of a ferrous type surface, such as aluminum alloys, copper alloys, tin alloys, lead alloys, moly alloys, and bronze alloys. These alloys can function as the metal matrix for composites that make up the alloy. Such composites can include nanoparticles, microparticles, and solid fillers, such as silicon, carbides, and oxides that contribute to durability and wear resistance. The ferrous type alloys are typically characterized by higher hardnesses that that of the non-ferrous type alloys. For example, iron (Fe, body center cubic allotrope) alloy typically has Vickers hardness of 608 MPa, while an aluminum (Al) alloy typically has a Vickers hardness of 167 MPa. For example, Silitec is a commercially available material that is a composite of silicon microparticles in a silicon-aluminum alloy matrix.

The following are examples of the present disclosure and are not to be construed as limiting.

Examples

Lubricant compositions of the present disclosure and comparative compositions are prepared and compared with each other with respect to lubricant performance.

Testing Method

SRV testing measures lubrication friction of a piston ring segment on a cylinder liner segment subjected to linear oscillation motion between the two segments. As such, an SRV Screener method is used to evaluate the cylinder liner/piston ring lubricant performance for the combination of Silitec (Si—Al alloy) cylinder liner and a nitrided steel piston ring. In all tests, the piston ring is of an iron alloy, specifically a nitride steel. The cylinder liner is an Si—Al alloy, specifically a Silitec silicon-aluminum alloy.

All test parameters are summarized in Table 2 below. An acceptable SRV test result is achieved when the value of the lubricant frictional coefficient is less than or equal to 0.31 at the end of the test time.

TABLE 2 Conditions of SRV Screener Method SRV Screener Frequency Stroke Tempera- Time Load Method [Hz] [μm] ture [C.] [min] [N] Specimen Single Run 20 3000 130 30 170 Oscillating Ring on Stationary Liner

Examples and Comparative Examples

Lubricant compositions with varying amounts of low base carboxylate detergents are tested using the SRV Screener Method. The results are set forth in Table 3 below.

TABLE 3 Effect of Carboxylate Detergents on the Measured Silitec SRV Frictional Coefficient Component wt % Ex 1 Ex 2 Ex 3 Ex 4 Ex 5 Ex 6 Additive System 12.7 12.7 12.7 12.7 12.7 12.7 Group IV base oil 30.0 30.0 30.0 30.0 30.0 30.0 Group III base oil 52.2 51.7 51.6 51.4 51.2 43.2 Group II base oil 1.68 1.68 1.68 1.68 1.68 1.68 ZDDP secondary alcohol derived 0.85 0.85 0.85 0.85 0.85 0.85 Low-base Ca salicylate detergent 0 0.4 0.45 0.62 0.82 11.56 (TBN ≦ 100 mg KOH/g) high/mid-base Ca salicylate 2.64 2.71 2.72 2.75 2.78 0 detergent (TBN > 100 mg KOH/g) Frictional Coefficient, 30 minutes 0.18 0.17 0.29 1.0 0.32 0.41 Acceptable SRV Frictional YES YES YES NO NO NO Performance ≦0.31 “A” value   $A = \frac{{wt}\mspace{14mu} \% \mspace{14mu} {low}\mspace{14mu} {base}\mspace{14mu} {carboxylate}\mspace{14mu} {detergent}}{\% \mspace{14mu} {base}\mspace{14mu} {oil}\mspace{14mu} {proton}\mspace{14mu} {aromaticity}}$ 0 123 141 193 252 3230

As shown in Table 3, formulations having less than 0.60 wt % low base salicylate detergent exhibit acceptable lubricant performance.

FIG. 1 is a plot of a ratio “A” vs. measured Silitec SRV frictional coefficients indicating the region of acceptable Silitec SRV frictional performance. “A” is defined as follows:

$A = \frac{{wt}\mspace{14mu} \% \mspace{14mu} {low}\mspace{14mu} {base}\mspace{14mu} {carboxylate}\mspace{14mu} {detergent}}{\% \mspace{14mu} {base}\mspace{14mu} {oil}\mspace{14mu} {proton}\mspace{14mu} {aromaticity}}$

The “A” ratios for the foregoing tests are plotted in FIG. 1. The results demonstrate that acceptable Silitec SRV frictional coefficient values (acceptable lubricant performance) are obtained for “A” values of less than or equal to 190.

Various lubricant compositions with and without aromatic Group V base oil are tested using the SRV Screener Method. The results are set forth in Table 4 below.

TABLE 4 Impact of Addition of Aromatic Group V Base oil on Measured Silitec SRV Frictional Coefficients Component wt % Ex 5 Ex 7 Ex 8 Ex 9 Ex 10 Additive System 12.7 12.9 12.7 12.7 12.7 Group IV base oil 30.0 0 30.0 30.0 30.0 Group III base oil 51.2 80.8 50.2 49.2 46.1 Group II base oil 1.68 1.88 1.68 1.68 1.61 Alkylated Naphthalene Group V base 0 0 1.0 2.0 5.0 oil ZDDP secondary alcohol derived 0.85 0.85 0.85 0.85 0.85 Low-base Ca salicylate detergent 0.82 0.82 0.82 0.82 1.25 (TBN ≦ 100 mg KOH/g) High/mid-base Ca salicylate 2.78 2.78 2.78 2.78 2.54 detergent (TBN > 100 mg KOH/g) Frictional Coefficient, 30 minutes 0.32 0.34 0.31 0.28 0.27 Acceptable SRV Frictional NO NO YES YES YES Performance ≦0.31 “A” value   $A = \frac{{wt}\mspace{14mu} \% \mspace{14mu} {low}\mspace{14mu} {base}\mspace{14mu} {carboxylate}\mspace{14mu} {detergent}}{\% \mspace{14mu} {base}\mspace{14mu} {oil}\mspace{14mu} {proton}\mspace{14mu} {aromaticity}}$ 252 225 2.1 4.1 1.3

Examples 5 and 7 differ by base stock composition and demonstrate that the Group III and Group III/IV base stock systems with the indicated additives do not provide acceptable lubricant performance for the iron alloy ring/Silitec liner. Examples 8, 9 and 10 contain the same additive system as examples 5 and 7, with varying levels of low base salicylate detergent and aromatic Group V base oil. The results demonstrate that acceptable or borderline lubricant performance is obtained when the calculated “A” values are less than or equal to 190.

Various lubricant compositions with varying amounts of aromatic Group II base oil are tested using the SRV Screener Method. The results are set forth in Table 5 below.

TABLE 5 Impact of Increasing Group II Base Oil Content on Measured Silitec SRV Frictional Coefficients Component wt % Ex 5 Ex 11 Additive System 12.7 12.0 Group IV base oil 30.0 28.5 Group III base oil 51.2 48.6 Group II base oil 1.68 6.59 ZDDP secondary alcohol derived 0.85 0.81 Low-base Ca salicylate detergent (TBN ≦ 0.82 0.78 100 mg KOH/g) High/mid-base Ca salicylate detergent 2.78 2.64 (TBN > 100 mg KOH/g) Frictional Coefficient, 30 minutes 0.32 0.28 Acceptable SRV Frictional Performance NO YES ≦0.31 “A” value   $A = \frac{{wt}\mspace{14mu} \% \mspace{14mu} {low}\mspace{14mu} {base}\mspace{14mu} {carboxylate}\mspace{14mu} {detergent}}{\% \mspace{14mu} {base}\mspace{14mu} {oil}\mspace{14mu} {proton}\mspace{14mu} {aromaticity}}$ 252 62

As shown in Table 5, increasing the Group II base oil and reducing the level of low base salicylate detergent to <0.8 wt % reduces the frictional coefficient to an acceptable level.

Various lubricant compositions with phenate detergents with varying TBN levels are tested using the SRV Screener Method. The results are set forth in Table 6 below.

TABLE 6 Impact of Phenolic Detergents on Measured Silitec SRV Frictional Coefficients Component wt % Ex 12 Ex 13 Additive System 12.65 12.65 Group IV base oil 30.0 30.0 Group III base oil 49.89 51.99 Group II base oil 1.61 1.61 ZDDP secondary alcohol derived 0.85 0.85 Low-base phenate detergent (TBN ≦150 mgKOH/g) 5.0 0 High-base phenate detergent (TBN >150 mgKOH/g) 0 2.9 Frictional Coefficient, 30 minutes 0.33 0.17 Acceptable SRV Frictional Performance NO YES ≦0.31

In Table 6, acceptable frictional performance is estimated when the phenate detergent concentration is 4.5% or less based on the total weight of the lubricant composition.

Tables 7 to 9 set forth possible formulations for lubricant compositions.

TABLE 7 Lubricant Compositions Component wt % Ex Ex Ex Ex Ex Ex Ex 14 15 16 17 18 19 20 Additive System 9.5 9.5 9.5 9.5 9.5 9.5 9.5 Group III/Group IV 80.7 80.7 80.7 80.7 80.7 80.7 80.7 base oil ZDDP secondary 0.80 0.80 0.80 0.40 alcohol derived ZDDP primary 0.80 0.80 0.80 0.40 alcohol derived Low-base 0.50 0.50 0.50 0.50 0.50 0.50 0.50 salicylate detergent high/mid-base 2.50 2.50 2.50 2.50 2.50 2.50 2.50 salicylate detergent Dispersant - 3.50 3.50 4.00 4.00 6.00 6.00 3.50 hydrocarbyl sub- stituted succinimide Dispersant - borated 2.50 2.50 2.00 2.00 2.50 hydrocarbyl sub- stituted succinimide ZDDP—Zinc dialkyldithiophosphates

TABLE 8 Lubricant Compositions Ex Ex Ex Ex Ex Component wt % 21 22 23 24 25 Additive System 15.5 15.5 15.5 15.5 15.5 Group III/Group IV base oil 80.0 81.0 50 68.0 71.0 Group II base oil 25 Group I base oil 5.0 Aromatic Group V base oil 2.0 Low-base salicylate detergent 9.5 11.5 11.5 low-base phenate detergent 3.50 high-base phenate detergent 4.50

TABLE 9 Lubricant Compositions Component wt % Ex 26 Ex 27 Ex 28 Additive System 9.5 9.5 9.5 Group III/Group IV base oil 76.2 80.2 73.2 Aromatic Group V base oil 5.0 Ester Group V base oil 5.0 1.0 3.0 Low-base salicylate detergent 0.59 0.59 0.59 high/mid-base salicylate detergent 2.74 2.74 2.74 Dispersant - hydrocarbyl substituted succinimide 3.50 4.00 3.50 Dispersant - borated hydrocarbyl substituted 2.50 2.00 2.50 succinimide

For purposes of this disclosure, the salicylate and phenate detergents can be the calcium and/or magnesium derivatives thereof.

All documents described herein are incorporated by reference herein, including any priority documents and/or testing procedures to the extent they are not inconsistent with this text, provided however that any priority document not named in the initially filed application or filing documents is NOT incorporated by reference herein. As is apparent from the foregoing general description and the specific embodiments, while forms of the disclosure have been illustrated and described, various modifications can be made without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the disclosure be limited thereby. Likewise, the term “comprising” is considered synonymous with the term “including” for purposes of Australian law.

All patents and patent applications, test procedures (such as ASTM methods, UL, methods, and the like), and other documents cited herein are fully incorporated by reference to the extent such disclosure is not inconsistent with this disclosure and for all jurisdictions in which such incorporation is permitted.

When numerical lower limits and numerical upper limits are listed herein, ranges from any lower limit to any upper limit are contemplated. While the illustrative embodiments of the disclosure have been described with particularity, it will be understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside in the present disclosure, including all features which would be treated as equivalents thereof by those skilled in the art to which the disclosure pertains. The disclosure has been described above with reference to numerous embodiments and specific examples. Many variations will suggest themselves to those skilled in this art in light of the above detailed description. All such obvious variations are within the full intended scope of the appended claims. 

What is claimed is:
 1. A lubricant composition, comprising: (A) 50 wt % or more of a base stock, based on the total weight of the composition, selected from the group consisting of a Group III base oil, a Group IV base oil, and a combination thereof and (B) one or more additional components selected from the group consisting of (i) one or more high or medium base carboxylate detergents; (ii) one or more low base carboxylate detergents, wherein the one or more low base carboxylate detergents is present at a level of 0.60 wt % or less, based on the total weight of the composition; (iii) one or more low base carboxylate detergents and one or more aromatics-containing base stock(s), wherein A is less than or equal to 190, wherein A is determined according to the formula $A = \frac{{wt}\mspace{14mu} \% \mspace{14mu} {low}\mspace{14mu} {base}\mspace{14mu} {carboxylate}\mspace{14mu} {detergent}}{\% \mspace{14mu} {base}\mspace{14mu} {oil}\mspace{14mu} {proton}\mspace{14mu} {aromaticity}}$  wherein wt % low base carboxylate detergent is determined by the weight based on the total weight of the composition, and wherein % base oil proton aromaticity is the percentage of aromatics present in the base oil; and (iv) one or more phenolic detergents, wherein if the one or more phenolic detergents is one or more phenate detergents, the one or more phenate detergent is present at a level of less than 5 wt % based on the total weight of the lubricant composition, wherein the lubricant composition exhibits a frictional coefficient of less than or equal to 0.31 in an SRV Screener Test.
 2. The composition of claim 1, wherein the base stock is present at 60 wt % or more based on the total weight of the composition.
 3. The composition of claim 1, wherein the base stock is present at 70 wt % or more based on the total weight of the composition.
 4. The composition of claim 1, wherein the one or more low base carboxylate detergents is selected from a group comprising alkylated mono-carboxylates, wherein the carboxylate functional group may include a carboxylic acid, an ester, an amide, an imide, an anhydride, a halide, or a salt.
 5. The composition of claim 1, wherein the one or more low base carboxylate detergents is an alkylated salicylate detergent.
 6. The composition of claim 1, wherein the one or more low base carboxylate detergents is an alkylated calcium salicylate detergent.
 7. The composition of claim 1, wherein the one or more phenolic detergents is a phenate detergent.
 8. The composition of claim 7, wherein the phenolic detergent is a calcium phenate detergent.
 9. The composition of claim 1, wherein the low base carboxylate detergent has a TBN of less than
 70. 10. The composition of claim 1, wherein the base stock is a combination of a Group III base oil and a Group IV base oil.
 11. The composition of claim 1, wherein the aromatics-containing base stock is a Group II base stock.
 12. The composition of claim 1, wherein the one or more aromatics containing base stock is a Group V base stock.
 14. A method for lubricating a surface of a Si—Al alloy, comprising applying to the surface the lubricant composition of claim
 1. 13. A method of lubricating a cylinder liner of a composite of silicon microparticles in a silicon-aluminum alloy matrix and a nitrided steel piston ring, comprising applying to rubbing surfaces of the liner and the piston ring the lubricant composition of claim
 1. 14. A method of lubricating rubbing surfaces of dissimilar metallic materials in which one rubbing surface has a higher Vickers hardness than the other rubbing surface, comprising applying to the rubbing surfaces the lubricant composition of claim
 1. 15. The method of claim 14, wherein the one of the metallic materials is a ferrous alloy and the other of the metallic materials is a non-ferrous alloy. 